A typical machine of this type includes a creel for supporting the spools, a delivery system which includes several feed rollers, and a first thread guide arranged before the delivery system along the strand paths, supported for back and forth movement parallel to the axes of the feed rollers, and having a guideway for each yarn strand. A thread-guiding mechanism follows the delivery system along the strand paths, a spindle is provided for supporting a winding bobbin, and a second thread guide is arranged along an extension of the axis of the spindle and has a guide eyelet therein for each yarn strand. A third thread guide is arranged below the second thread guide and has an opening through which all the yarn strands pass together.
The known ring twisting machines of the above-mentioned type are not well-suited for use with filament yarn strands made of aramid (aromatic polyamide), for example, that which is presently available under the trademark "Kevlar". Aramids have, based on their molecular structure, an extremely small capacity to stretch and a very high tensile strength. Twisted yarns of aramid are therefore used in products which must remain pliable under high tensile loads, for example car tires and drive belts. The processing of aramid fibers to produce a twisted yarn requires special measures with respect to the thread-guiding parts, since the fiber, in a nontwisted condition, can be seriously affected by damage to its surface. If damaged, a strong notching effect occurs, as in the case of steel, which considerably reduces the strength of the fiber. Furthermore, because of the minimal capacity of aramid fibers to stretch, it is important that all individual fibers in any part of the finished twisted yarn have, as much as possible, the same length, so that they carry a load as equally as possible. Uneven lengths of the fibers can cause an overload of the shorter fibers and tearing thereof when the yarn is stressed, since the longer fibers carry no load at all.
A production speed which is as high as possible is desired for economical manufacture of the twisted yarn. However, the higher the production speed, the greater the danger of damage of the filaments and movement of the filaments which causes them to be twisted into the yarn with uneven lengths. In known twisting machines, a danger of yarn damage is present primarily at the reciprocating thread guide provided along the strand paths between the spools and the delivery system. This known thread guide has, as guideways for the individual yarn strands, wire bars, on which the yarn strands are relatively sharply deflected. This can result in filaments being either moved or damaged. Furthermore, damage of the filaments can occur at the thread-guiding mechanism which follows the delivery system, since in the known system it is a simple, fixedly supported rod.
A basic purpose of the invention is therefore to provide a twisting machine of the above-mentioned type in which the manufacture of twisted yarn from filament yarn strands is possible at high speeds, but in which damage, movement and irregular feeding of the filaments is avoided.